To morphologically investigate the mechanism by which vitamin A alters epidermal cell differentiation with resultant inhibition of keratinization. Chick metatarsal skin is cultured in vitro and stimulated to undergo mucous metaplasia by vitamin A acid at varying doses. Specimens are taken at varying time intervals and evaluated for mucin production by the use of special strains, such as PAS 9 with and without distase), Alcian Blue, Toluidine Blue, and Colloidal iron. Specimens are also fixed in glutaraldehyde for subsequent examinations under the transmission and scanning electron microscopes.